The present invention is concerned with an integrated semiconductor circuit which comprises a microprocessor and an analog-to-digital converter which is in turn controlled by an analog input signal to be interpreted by the microprocessor and by at least one analog reference voltage.
The reference "Siemens Forschungs- und Entwicklungsberichte", Vol. 8 (1979) No. 5, pages 261-263, incorporated herein by reference, can be cited as prior art. It is pointed out therein that the increased use of digital control electronics in the form of microprocessors and microcomputers requires analog-to-digital converters and digital-to-analog converters in a correspondingly increased scope as interfaces between the analog environment and the computer. Converter modules that are manufactured in the same technology as the microprocessors and can thus be co-integrated on the computer chip are of particular interest. In the interests of high converter speed, it is recommended to employ converters which function according to the principle of step-by-step approximation (=successive approximation). It is also advantageous when the precision or scaling network required given analog-to-digital converters functioning according to the principle of successive approximation is realized by means of a capacitance network consisting of MOS capacitors (instead of the resistance network, for example an R/2R network, that is otherwise standard). Details with respect to this are cited in the above mentioned reference.
A monolithic combination of a single-chip computer and an analog-to-digital converter is thus applied for the control of events that produce analog process quantities. The integrated A/D converter is usually responsible for a plurality of analog measuring points which, depending on the respective information generators employed at the measuring points, have different, non-coinciding, analog voltage ranges. This, however, means that the full resolution of the converter (often 8 bit) cannot be fully exploited for a measuring point.
In order to resolve the problem just pointed out above, the analog-to-digital converter that is co-integrated on the computer chip could be provided with a correspondingly higher resolution, for example with a resolution of 10 bits, than is required per se for the individual measuring points. The analog process quantity converted with, for example, a width of 10 bits is then brought to the desired size having a smaller bit width by means of scaling algorithms by use of the computer program.